Dynamic focusing circuit for a CRT and display apparatus incorporating same
US6018222A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | May 11, 1998 |
| Grant date | Jan 25, 2000 |
| Priority date | — |
| Expiry date | May 11, 2018 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04N3/26
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
The invention relates to a dynamic focusing circuit with an output (1) for supplying a dynamic focusing voltage (Vf) to a focus electrode of a cathode ray tube (CRT). The dynamic focusing voltage (Vf) has, in succession, a falling edge, an almost flat part and a rising edge. A first transistor (T1) has a main current path (c1, e1) coupled between a supply voltage (V+) and the output (1). An arrangement of a secondary winding (Ls) of a transformer (T) and a current determining circuit (12) is coupled between the control input (b1) of the first transistor (T1) and the output (1). The current determining circuit (12) supplies a bias current (Ib). A second transistor (T2) has a control electrode (b2) for receiving an input voltage (Vi) related to a parabolically shaped input waveform (Vin), and a main terminal (c2) coupled to the control input (b1) of the first transistor to withdraw current (Id) from the control input (b1). The secondary winding (Ls) supplies a voltage superposed on the dynamic focusing voltage (Vf). The voltage supplied by the secondary winding (Ls) and the current determining circuit (12) are dimensioned so as to minimize dissipation for driving the first transistor…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.